A Tornado jet from RAF Marham came within 100ft of a paramotor, narrowly avoiding a collision.
Details of the near miss have emerged in a report by aviation officials.
It says the warplane was circling over March, Cambs, prior to performing a flypast at Marham, in June.
It adds: 'A paraglider [later found to be a paramotor] was seen
to pass down the right-hand side of the aircraft, at the same level, and displaced by an estimated 50 - 100ft. Due to the late sighting, no evasive action was taken.'
The UK Airprox Board report says the paramotor pilot had taken off from March Aerodrome and climbed to 1500ft, before heading towards Holbeach.
'He had been in the cruise for about 3 - 4 minutes when he saw a Tornado pass him in his 10 o'clock, at the same height and heading as he was,' it adds.
'He noted that because it approached him from behind, he hadn't seen it earlier. he watched it initially remain on heading before making a 90-degree turn right, heading towards King's Lynn.'
Both pilots assessed the risk of collision as 'high'. An RAF investigation found that the paramotor did not appear on Marham's radar, so air traffic control could not warn the Tornado crew that the 950mph jet was approaching it.
Paramotors flying from March have since been fitted with high-powered strobe lights, to make them easier for the pilots of other aircraft to see.
The report also noted that a representative from the airfield had not attended meetings of the East Anglia Airspace User Working Group (EAAUWG), which includes both military and civilian users.
'It was agreed that the Fenland Centre would be invited to the next EAAUWG in order to promote a better understanding of operating practices and a potential means to deconflict movements,' it adds.
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